1. Field of the Invention
The present invention relates to a camera, a data printing device (to be referred to as a data back hereinafter) capable of being mounted on the camera and of printing various data on a film loaded in the camera, and a film winding device assembled in the camera.
2. Related Background Art
In a camera system in which a camera and a data back which does not communicate data with the camera are combined to perform a photographing operation, the data back changes a data printing time in accordance with a data printing signal from the camera, a transmission time of which changes depending on a film sensitivity. In this system, since signal processing of the data back is not complicated, if the transmission time of the data printing signal transmitted from the camera to the data back changes, no problem is posed.
Meanwhile, a camera system in which a camera and a data back which communicates data with the camera are combined to perform a photographing operation is also known. A camera system of this type which has various functions realized by serial data communication between a camera and a data back is disclosed in Japanese Patent Laid-Open (Kokai) No. 61-167934.
However, in this system, since signal processing of the data back is complicated, if the transmission time of the data printing signal transmitted from the camera to the data back changes, an erroneous operation may be caused by the change in transmission time.
It is a first object of the present invention to provide a camera which can prevent an erroneous operation when a camera and a data back which does not communicate data with the camera are combined or when a camera and a data back which communicates data with the camera are combined.
The following problem is posed when an inexpensive data back having a data communication function is manufactured. Data which is printed first by the data back is "year, month, and day" data. For this purpose, the data back employs a microcomputer on the basis of oscillation at 32 kHz. However, a microcomputer used in a camera requires high-speed processing, an oscillator of 4 to 8 MHz is employed. When data communication is to be performed between the microcomputers, a data communication speed must be determined in correspondence with a microcomputer having a lower data communication speed. Since a data communication time is about several tens of ms although it varies depending on the number of data, a frame speed tends to decrease, thus posing a problem. Of course, the microcomputer of the data back may be operated at a clock of about 4 to 8 MHz when the camera is activated, and may be operated at a clock of about 32 kHz when the camera is inactivated. In this case, an arrangement is complicated or an expensive microcomputer must be used. It is therefore a second object of the present invention to provide a camera system capable of performing data communication which does not adversely influence a frame speed with an inexpensive arrangement.
A conventional camera with an electric winding device is arranged to perform a film winding operation immediately after exposure of an object for a preset shutter time is completed. When a data back is mounted on the camera and a low-sensitivity film is used, a data printing operation is required for a long period of time. However, when exposure of an object is completed, the data printing operation is interrupted, and a film winding operation is performed. With this sequence, printed data can be prevented from being blurred upon film movement.
However, according to the above technique, although printed data can be prevented from being blurred, the density of the printed data is low due to a short printing time, and cannot often be discriminated. This phenomenon is conspicuous as the shutter time is shorter or a film sensitivity is lower.
It is a third object of the present invention to solve this problem.